Cellular resistance to chemotherapeutic agents is a major obstacle in the treatment of human cancers. Efflux pumps, specifically P-glycoprotein (Pgp) and multidrug resistance protein (MRP) subfamily members contribute to drug resistance by directly effluxing anticancer drugs from cells. MRP subfamily members transport glucuronidated and glutathione conjugated substrates, and confer resistance to a wide range of agents including anthracyclines, epipodophyllotoxins, vinca alkaloids, and nucleotide analogs. Our laboratory has shown that MRP7 is competent in the transport of amphipathic anions, using membrane vesicles, the MgATP dependent transport of 17 p-estradiol-(17-p-D-glucuronide) (E217BG) was established. Further, our previous work has demonstrated that MRP7 has a resistance phenotype which is distinct from other MRP family members: in that MRP7 is the only member of this group to confer resistance to taxanes. MRP7 is only the second pump to demonstrate this resistance, the first identified pump conferring this resistance is Pgp. Taxanes are used primarily in the treatment of ovarian, lung and breast cancer. To date, all of the functional information gathered about MRP7 has been acquired using in vitro model systems. Since MRP7 has a distinct phenotype and has the lowest homology to MRP1 of all the MRP subfamily members, it is of interest to determine the biochemical parameters which are responsible for its activities. Further, biochemical and structural information that would be critical to the rational design of inhibitors or modulators has not yet been elucidated. This proposal will outline plans to elucidate the role MRP7 plays in the in vivo resistance phenotype of this protein using a knockout mouse model that we developed. The second aim will elucidate the specific biochemical activities that are required for MRP7 unction. For example, the specific biochemical activities related to binding, ATP hydrolysis and modulation of the activities which are involved in MRP7's ability to transport drug. The third aim will characterize the structural elements required for MRP7 function. By using a combination of in vivo and in vitro approaches, these aims will lend insight into this recently discovered resistance factor. It is important to have an understanding of the proteins that lower the effectiveness of chemotherapeutic agents used to treat cancer patients. The goal of this proposal is aimed is to obtain information about one of these recently identified proteins.